1. Cross Reference
This Application is related to my commonly-assigned U.S. Pat. No. 3,734,068, "Fuel Injection Control System", issued May 22, 1973, my co-pending commonly-assigned U.S. application for Patents Ser. Nos. 226,486 entitled "RPM Information Signal Generating Circuitry for Electronic Fuel Control System" filed Feb. 15, 1972, 226,496 "Electronic Fuel Control System Including Means for Providing a Continuous Variable Correction Factor" filed Feb. 15, 1972, 729,317 "Roughness Sensor" filed Oct. 4, 1976, now Pat. No. 4,092,955, and commonly-assigned Application 790,625 "A Speed Sensitive Electronic Fuel Control System for an Internal Combustion Engine" filed Apr. 23, 1977, now Pat. No. 4,195,599. The disclosures of each of the above cross-referenced cases being expressly incorporated herein by reference.
2. Field of Invention
The invention is related to electronic fuel control systems for internal combustion engines and in particular to speed sensitive electronic fuel control systems of the type taught in U.S. Pat. No. 3,734,068, and my pending applications Ser. Nos. 226,486 and 226,498 cited above using the charge transfer circuit of the type disclosed in my commonly-assigned co-pending application Ser. No. 729,317.
3. Prior Art
The speed sensitive electronic fuel control disclosed by Reddy in U.S. Pat. No. 3,734,068 and improvements thereto as disclosed in patent application Ser. Nos. 226,486 and 226,498 cited above, is illustrated in FIG. 1. This system embodies two capacitances 10 and 12 which are sequentially charged from two current sources respectfully designated RPM Signal Generator 14 and Ramp Signal Generator 16. Electronically actuated switches, illustrated by mechanical ganged switch 18, controlled by an output signal from Switch Circuit 20, connects the two signal generators 14 and 16 to capacitances 10 and 12 in a manner so that when capacitance 10 is being charged by the RPM Signal Generator 14, capacitance 12 is being charged by Ramp Signal Generator 16 and vice versa. In this manner, both capacitances are sequentially charged, first by the output of the RPM Signal Generator 14, then by the output of the Ramp Signal Generator 18. At the end of each sequential charging period, the capacitance having been last charged by the output from the Ramp Signal Generator 16 is discharged by means of a Discharge Circuit 22 to a predetermined value prior to the initiation of a new charging sequence.
The Switch Circuit 20 may be a simple bi-stable flip-flop producing a square wave output signal in response to trigger signals designated TR 1 and TR 2. These trigger signals may be derived from the engine's crankshaft, flywheel or ignition system, and are indicative of predetermined angular positions of the engine, normally 180.degree. apart. Switch 18 responds to this square wave signal and assumes a first position in response to the positive portion and a second position in response to the ground or negative portion of the signal. Discharge Circuit 22 responds to the positive and negative transitions of the square wave and discharges the appropriate capacitance. The potential developed across both capacitances as they are being charged are communicated to the negative input of Comparator 24 by means of diodes 26 and 28. The output of a Load Signal Generator 30 is applied to the positive input to the Comparator 24. The Load Signal Generator 30 may be a pressure sensor generating a signal indicative of the pressure in the engine's air intake manifold as taught by Reddy in U.S. Pat. No. 3,734,068 or any other sensor generating a signal indicative of the engine's load.
The output of the comparator 24 is connected in parallel to the inputs of two AND gates 32 and 34. The square wave output of the Switch Circuit 20 is applied directly to the alternate input of AND Gate 32 and indirectly to the alternate input of AND Gate 34 by means of an Inverting Amplifier 36. Alternately, the reciprocal or complementary square wave signal generated by the flip-flop may be applied directly to AND Gate 34.
The operation of this prior art circuit is described with reference to FIG. 1 and the waveforms shown on FIGS. 2A and 2B. It is assumed the Switch Circuit 20 is triggered by trigger signal TR 1 and its initial output signal is positive as shown on FIG. 2A. The positive output signal from the Switch Circuit 20 actuates switch 18 to the position shown on FIG. 1, activates Discharge Circuit 22 to discharge capacitance 12 to the predetermined value and enables AND Gate 32. Gates 32 or 34 communicate the output of the Comparator 24 to either Fuel Injector Group 1 or Group 2 depending upon which of the two AND gates is enabled by the square wave signal generated by the Switch Circuit 20.
The waveforms shown on FIG. 2B illustrate the change in the output 46 from the Comparator 24 when the engine speed has increased accompanied by an increase in the value of the load signal 44. The positive portion of the signal 46 is changed by two factors. Increasing the value of the load signal increases the positive portion of the Comparator's output by a first factor designated by the cross hatches area designated "a" indicative of the increased time it takes for the potential across capacitances 10 or 12 to reach the higher value of the load signal 44. The positive portion of the output signal generated by the Comparator 24 may also be changed as a function of engine speed since the final value of the charge capacitances 10 or 12 during the first interval varies with time. Obviously, if the only change in the waveforms illustrated on FIG. 2B was an increase in engine speed without a corresponding change in the load signal, the positive portion of the output from Comparator 24 would increase or decrease depending on whether the voltage on capacitance 10 or 12 at the end of the first charging is lower or higher than the voltage at the prior lower speed. The change in the output signal would be indicative of the change in the value of the charge on capacitance 10 or 12 at the end of the first charging period. Conversely, if the only change was an increase in the load signal without a corresponding change in the engine speed, the change in the positive portion of the output from Comparator 24 would only be proportional to the difference in time it would take the Ramp Signal Generator to charge either capacitance to the new value of the load signal.
Although this circuit works extremely well, it requires that the two capacitances 10 and 12 be a matched pair (identical) which require that they be tested prior to assembly to assure that the output signals generated by the Comparator 24 will be identical within permitted tolerances. Further since both capacitances are charged by both the RPM and Ramp Generators, a severe restraint is placed on both signal generators to produce the desired waveforms. The disclosed invention eliminates both of these deficiencies.